Xanthation process



Aug. 6, 1957 A. ROBERTSON 2,801,998 mummxon PROCESS Filed April 2a, 1953 INVENTOR 11nd? 'ew 1Z0 bcrtson BY wzm ATTORNEY,

United Statcs PatcntlOfilicc 2,801,998 Patented Aug. 6, 1957 XANTHATION PROCESS Andrew Robertson, Richmond, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware filamentary yarns and cords of regenerated cellulose by the viscose process. More particularly, it is concerned with the steps of xanthating alkali cellulose and dispersing the cellulose xanthate to form the viscose spinning solution used in the process.

One of the persistently sought objects in viscose rayon manufacture is the production of yarn having increased resistance to fatigue without sacrifice in tenacity. This object is of special and critical importance in the manufacture of rayon tire cords. The cores used in tire manufacture must be able to withstand the constant flexing to which they are subjected during actual use.

An object of the present invention is to provide improved methods for producing viscose of high filterability. Another object is to produce viscose suitable for spinning into yarn of high resistance to fatigue. Another object is to provide more economical methods for producing such viscose with conventional equipment. Other objects of the invention will become apparent from the following specification and claims.

The single figure of the drawing is a plan view of a suitable xanthating-mixing apparatus for carrying out one modification of the process of the present invention.

According to the process of this invention highly fatigue-resistant yarns are produced by a critical modification of the conventional process for preparing the viscose spinning solution. In the conventional preparation of the viscose spinning solution, cellulose, in the form of sheets of wood pulp, cotton linters, etc., is soaked in a caustic alkali solution until thoroughly saturated. The caustic is drained and a hydraulic ram compresses the mercerized sheets, squeezing out excess caustic until the press weight ratio (weight of wet pressed pulp divided by the weight of air-dry pulp originally charged) is about 3 to l. The alkali cellulose formed is shredded into fine crumbs in a closed vessel where rotating S-shaped blades simultaneously cut and mix the alkali cellulose. The alkali cellulose crumbs are then fed into a rectangular steel container for aging. After being aged to provide the desired ultimate viscose viscosity, the crumbs are dropped into a hexagonal steel xanthating drum called a baratte. The baratte is revolved; carbon disulfide is added; and the white mealy substance becomes yellow and sticky as the alkali cellulose is transformed into cellulose xanthate. After substantially complete reaction with the carbon disulfide present, the Xanthatcd alkali cellulose is fed into a mixer or dissolving machine.

The mixer is a brine-jacketed tank containing eificient stirring and shearing members. Before receiving the xanthate, the mixer is filled with a measured quantity of dilute caustic soda solution. In this caustic solution the Xanthate gradually dissolves to form the viscose spinning solution. The viscose solution is filtered, deaerated and permitted to ripen at temperatures of l8-20 C. Viscose modifiers, as described in Cox, U. S. Patent Nos. 2,535,044 and 2,536,014, may be added and thus reduce ripening time. The viscose spinning solution is pumped to the spinning room and extruded through spinnerets into a coagulating and regenerating bath of the Muller type,

usually containing sulfuric acid, sodium sulfate and zinc sulfate. The yarns produced are then stretched in the presence of hot dilute acid and may be collected in a bucket or on a bobbin, or they may proceed directly to subsequent treatments without being collected as in the conventional continuous process. The yarns are subsequently purified, slashed and processed into tire cords in the usual manner. 7

In the process of the present invention the viscose spinning solution is also prepared by the addition of carbon disulfide to alkali cellulose with subsequent dilution. However, the xanthation with carbon disulfide is performed in two steps: The alkali cellulose is only partially xanthated in the dry phase (as-aged condition) and then the xanthation is completed after the partially xanthated alkali cellulose has been mixed with a dilute (about 540% concentration) aqueous caustic solution to give a cellulose content of 4 to 15%.

It has been found that the objects of this invention can best be achieved by first partially xanthating the alkali cellulose in the baratte until a xanthate sulfur substitution of at least 13% is obtained. The xanthate sulfur substitution is defined as the percent sulfur that has reacted with the alkali cellulose divided by the percent cellulose in the mass multiplied by 100. In accordance with a preferred embodiment of the invention the partially xanthated material is then dispersed in sufiicient aqueous caustic solution to give a cellulose content of 4 to 10% and an alkali content of 4 to 8%. To this dispersion suflicient carbon disulfide is added so that at least 10%, preferably 15%, of the total xanthate sulfur substitution ultimately obtained is accomplished during this dispersion phase. In other words, a maximum of 90%. preferably not more than of the total xanthate sulfur substitution occurs in the initial phase. By maintaining the limits on xanthation described, fatigue resistances of the cords produced have been improved over 60%.

The initial xanthation has been termed dry phase Xanthation and may be accomplished in a conventional baratte; the final or dispersion phase xanthation may be accomplished in a conventional viscose mixer. It is necessary to accomplish a partial xanthate substitution of at least 13% in the dry phase" in order to prepare a spinnable viscose solution of satisfactory filterability. Filterability is measured quantitatively by determining the number of grams of viscose solution of a specified composition which will pass through a A square inch area of standard filter press dressing in 60 minutes under a pressure of 60 pounds per square inch (gage) at a temperature of 18 C. using a viscose adjusted to contain 7% cellulose and 6% caustic soda. Unless this partially xanthated material, when dispersed in caustic solution to a cellulose content of 4 to 10%, is further xanthated to the extent of at least 10 to 15% of the total xanthate sulfur substitution, the desirable improvement in fatigue resistance mentioned will not be obtained by splitting the xanthation.

After the alkali cellulose has been xanthated in two steps in accordance with this invention, referred to herein as split xanthation, the viscose spinning solution prepared is treated in the conventional manner described above.

A modification of the preferred process makes possible the preparation of viscose spinning solution directly from alkali cellulose in a single vessel. The use of a single vessel has obvious attendant advantages. Since both xanthation and dissolving are accomplished in the same machine the hazard to the workers due to the release of carbon disulfide vapor is considerably reduced. Another advantage is that it permits the double process to be completed in a much shorter time.

Processes have been proposed for xanthating and min.

ing to form viscose in a single vessel. However, none of the processes heretofore proposed has been economically practicable for producing satisfactory viscose spinning solution. In such previous processes the viscose tends to be unduly viscous during its formation, requiring excessive power and special expensive xanthator-mixers to mix it. Mixing may be facilitated by drastically degrading the cellulose, but this is quite undesirable because it results in an inferior yarn. Extremely low temperatures have been suggested as a way of overcoming some of the difficulties of a one-vessel process, but this is expensive and has not prevented the formation of poorly filterable, nonuniform dispersions.

By carrying out the xanthation in two steps in any suitable xanthator-mixer in accordance with critical conditions it has been found possible to produce viscose from alkali cellulose in a single inexpensive piece of equipment without resorting to excessive power for mixing, or unusually low temperatures, or degradation of the cellulose. In the first step a dry phase xanthation of alkali cellulose is conducted until at least 13% and not more than 19% xanthate sulfur substitution has occurred. The partially xanthated alkali cellulose crumbs retain substantially the form of the dry alkali cellulose crumbs. When this critical percentage of xanthation has occurred, a dilute solution (usually 540%) of sodium hydroxide is added to form an adherent plastic mass or dough having a cellulose content of from to and preferably from 10.5 to 14%. A dough phase xanthation is then conducted until the desired degree of xanthate sulfur substituticn has taken place and water is then added to form a viscose spinning solution of the usual concentration for spinning or casting. To realize the improvement in fatigue resistance of the cords ultimately produced, it is necessary to observe the critical precaution previously described for the process using separate xanthator and mixer. Unless the partially xanthated mate rial, when transformed into a dough phase, is further xanthated to the extent of at least 10 to 15% of the total xanthate sulfur ElliiQt'llLlllUlL, the desirable improvement is not obtained. The carbon disulfide for the dough phase" xanthation may be added separately, but it is usually preferable to add all that will ultimately be needed at the start of the dry phase xanthation. This amounts to at least 27.5 ,n of carbon disulfide based on the weight of dry cellulose in the original charge. After the critical xanthate sulfur substitution of 13 to 19% has occurred, the caustic solution is added rapidly, within not over 10 minutes, and reaction of the remaining carbon disuliide with the alkali cellulose continues in the dough phase" to the extent of at least 10 to 15% of the total xanthate sulfur substitution.

Adequate mixing should be provided during both dry and dough phase xanthation. Any suitably sized closed vessel, equipped with a substantial stirring member and means to seal and to evacuate or purge the vessel before adding the carbon disulfide, may be used. A suitable vessel of the ribbon blender or ribbon mixer" type is shown in the drawing. This comprises a long, generally hemieylindrical vessel 10 which is closed by bolting on a top. The closed vessel may be evacuated through pipe 12. For safety, the mixer is evacuated to 2428 inches of mercury after charging with alkali cellulose before carbon disulfide is introduced. Instead of evacuating the vessel it may be purged with nitrogen before adding carbon disulfide. A shaft 14 extends axially through the vessel and is arranged to be rotated at moderate speed by suitable means, a pulley 16 being indicated. Mounted on the shaft are a number of spoke-like supports 18 for the mixing elements. The mixing elements comprise two helical ribbon flights 20 and 22, mounted one within the other on the rigid supports 18. One ribbon flight has a righthand screw and the other a left-hand screw, so that the material is moved toward one end of the vessel by one flight and in the opposite direction by the other, thereby providing positive and thorough mixing. Other suitable vessels for use as xanthator-mixers will readily occur to one skilled in the art.

Certain critical distinctions will be apparent between the two modifications of split xanthation discussed. In both a partial dry phase xanthation is conducted and the xanthate sulfur substitution must be at least 13%; a markedly inferior filterability in the final viscose results from lesser xanthation. This initial xanthation step must not proceed beyond 19% xanthate sulfur substitution when the final xanthation is to be conducted in a dough phase, i. e., having a cellulose content of 10 to 15% as in the xanthatonmixer. If the dry phase xanthation is continued beyond 19% the viscose solution obtained via a dough phase final xanthation contains lumps of undissolved xanthate and is, in general, of quite unsatisfactory quality. This 19% upper limit need not be observed when the final xanthation is to be conducted in a dispersion phase, i. e., having a cellulose content of 4 to 10% in a mixer. This difference in procedure is explained in the following paragraph.

Before adding the partially xanthated alkali cellulose crumbs to the mixer, the dilute caustic solution is made to circulate through the mixer. The crumbs are fed in relatively slowly. By adding the crumbs slowly to the dilute solution, the crumbs are uniformly wetted. The resulting solution is then made to circulate past plates of close clearance by an efiicicnt stirring member. The result of this operation is to minimize the amount of lumps in the final viscose spinning soltuion. In the xanthator-mixer, where only one vessel is used, the extent of mixing is limited by space and the nature of the operation. The formation of a dispersion phase by feeding the partially xanthated alkali cellulose crumbs into a dilute caustic solution is not possible in a single vessel process. It is only possible where a second vessel to which the caustic solution may first be added, is used. In the single vessel process. it has been found that if all the diluting solution is added at once, reaction with the crumbs is incomplete. Only the outer surfaces of the crumbs are wetted. Special expensive shearing cquipmcnt requiring excessive power is usually necessary to cause penetration of the crumbs by the liquid and the formation of a satisfactory solution. I have found that if a dough phase is first formed by partial addition of the diluting solution prior to completion of xanthation and prior to final dilution with water, as described, less power and less expensive equipment can be used.

In both cases, the second phase of xanthation must begin when the material is at least 10 to 15% short of the total xanthation substitution ultimately desired. Unless at least 10 to 15% of the total xanthate sulfur substitution and preferably at least 15% occurs in the second stage, merely splitting the xanthation will not result in an improvement in the fatigue properties of the yarn produced.

The invention will be more clearly understood by referring to the examples and the discussion which follow. In the following examples the resistance to fatigue was measured by a so-called dynamically-balanced (DB1 fatigue tester. After conditioning for 48 hours at 21 C. and 60% relative humidity, a single cord is placed between two jaws that have been set 30 inches apart. The cord is then permitted to attain a temperature of C. by standing in the machine for about /2 hour. The tester then stretches the cord 3,000 times per minute using a stroke of .048 inch. The number of minutes during which the cord will withstand this treatment without breaking is called the DB fatigue.

EXAMPLE 1 Several viscose spinning solutions were prepared as follows:

Cellulose, in the form of wood pulp sheets, was

steeped in a 19% sodium hydroxide solution. The alkali cellulose shcets formed were pressed to expel excess caustic solution to a press weight ratio of 2.8 to l. The sheets were then shredded into fine crumbs, which were fed into a closed container to age. After being aged sufiiciently to produce an ultimate viscose viscosity of approximately 40 pulses (when meansured at 20 C.), the crumbs were dropped into a conventional xanthating baratte. Tests A through D illustrate a systematic variation in xanthating procedure.

Test A illustrates the conventional process. Carbon disulfide was added to the baratte and the baratte was revolved to stimulate reaction. After 90 minutes the xanthate sulfur substitution had reached 20.5 (based on the weight of cellulose charged to the steeping press). The xanthated alkali cellulose was then introduced into the mixer. The mixer had previously been charged with proper quantities of sodium hydroxide solution to pro duce a viscose containing 7.00% cellulose and 6.00% sodium hydroxide. The viscose solution was then removed from the mixer and permitted to ripen. During ripening it was filtered and deaerated. The spinning solution was then pumped to the spinning machine.

in tests B through D the xanthation environment was split between the baralte and the mixer as illustrated in Table I. After substantially complete reaction with the various amounts of carbon disulfide fed into the baratte, the partially xanthated alkali cellulose crumbs were in troduced into the mixer. The mixer had previously been charged with SUfilClBI'li caustic solution to produce a viscose containing 7.00% cellulose and 6.00% sodium hydroxide. The mixtures of tests B through B were agitated for aproximately 10 minutes to produce a uni form dispersion. Then the remaining quantities of carbon disulfide were added to produce eventually a xanthate sulfur substitution of 20.610296. Mixing was continued for 180 minutes. The viscose solution was then removed from the mixer and permitted to ripen. During ripening it was filtered and deaerated. The viscose spinning solution was then pumped to the spinning machine.

From the spinning machine through final processing into tire cords, the solutions of tests A through D all underwent identical treatment. They were spun into 1650 denier yarn by extrusion through spinnerets into a coagulating and regenerating bath composed of 9% sulfuric acid, 22% sodium sulfate and 5% zinc sulfate. The yarns were purified, slashed and processed into tire cords in the usual manner. Physical properties are presented in Table I.

The resistance of the cords to fatigue was improved from 45% to 65% by splitting the xanthation in accordance with the process of this invention without any deleterious effect on the tenacity.

Table I Viscose Composition Test A Test 13 Test C Test D Percent Cellulose 7. 7. 00 7. 00 7. 00 Percent Caustic 6. 00 6.00 6. 0O 6. 00 Percent. Xanthnto Substitution Aocornp. in Dry Crumb Stage 20.5 17.3 14.9 13.0 Percent Xanthate Substitution Aceomp. in Dispersion Phase 0 3.1 5.9 7. 6 Percent of Total Xanthate Subst.

Aecnrup. in Dispersion Phase 0 15. 2 28. 4 36. 9 Total Percent Xanthate Substitution. 2i]. 5 20. 4 2). 8 20. 6 Slashed Yam Properties (3650 De- Dry Tenacity (g. p. d.) 3.62 3.68 3. 71 3. 64 Dry Elongation (Percent). 10. 2 10.0 10.2 10.8 Tire Cord Properties (2 Ply Cords):

Twist (singles) 10.8 10. 8 10. 8 10. S Twist (cord) 11.2 11.2 11.2 11.2 Tenueity-Contiltioned (g. p. d.) 2. 67 2. 75 2, 71 2. 69 Tenaeity0ven Dry (g. p. (1.)", 3. 21 3. 20 3. 22 3. 19 Elongation at 15 lbs. teond.). 9. 8 9. 4 9. 6 9. 7 D. B. Fatigue (minutes) 1'12 94 90 102 6 EXAMPLE 2 Cellulose, in the form of wood pulp sheets, was steeped, shredded and aged as in Example 1.

In the split xanthation partial xanthation was carried out in the baratte until a xanthate substitution of 13.8% was obtained. The partially xanthated cellulose was introduced into the mixer. After mixing to produce a substantially uniform dispersion, sufi'icient carbon disulfide was admitted to cause a further xanthate substitution of 6.5%. The viscose was filtered, deaerated, ripened and then spun.

In conventional xanthation the procedure for xanthating alkali cellulose described in test A of Example 1, was followed.

Both solutions displayed a total xanthate substitution of 20.3%. They were spun into 2200 denier yarns by extrusion through spinnerets into a coagulating and regenerating bath composed of 8.7% sulfuric acid, 22% sodium sulfate and 5% zinc sulfate. The yarns were stretched between an out-of-bath roller and the bobbin upon which it was collected. The yarns were purified, slashed and processed into tire cords in the conventional manner. Physical properties are presented in Table II.

It should be noted that by splitting xanthation in accordance with the process of this invention, the resistance to fatigue is improved over 60% without sacrificing tenacity.

Table 11 Split Conven Viscose Composition Xanihational tion Xantha til ID Percent Cellulose 7. 00 Y. [)0 Percent Caustic 6. 00 6. 00 Percent Xanthate Substitution Aecomp in Dry Crumb Stage 13. 8 an. 3 Percent Xanthate Substitution Accord n Dispersion Phase 6. 5 0 Percent of Total Xanthate Substitution Aeeomp. in Dispersion Phase 32. 1 0 Total Percent Knuth-ate Substitution at End of Dissolving Stage 2ft. 3 20.3 Slashed Yarn Properties (2200 Denier):

Dry Tenacity (g. p. d.). 3.82 3. 78 Dry Elongation (Pereent)... 10. 2 10. 3 Tire Cord Properties (2 Ply Cords) Twist (singles) 10.4 it). 2 Twist. (cord) 8. 2 8. 2 Tenacity-Conditioned (g. p. d.) 3.01 2. 91 Tenacity-Oven Dry (g. p. d.). 3. 49 3. 45 Elonigation at 20 lbs. (condltloned) 8. 4 8. 5 DB atigue (Minutes) 117 78 The previous examples have been concerned with dispersion phase split xanthation in two vessels. The following examples illustrate dough phase split xanthation in a single vessel.

EXAMPLE 3 Cellulose, in the form of cotton linter sheets, was steeped in 19% sodium hydroxide solution. The alkali cellulose sheets formed were pressed to expel excess caustic solution to a press weight ratio of about 3 to 1. The sheets were then shredded into fine crumbs, which were fed into a closed container to age. After aging, a portion of the crumbs was dropped into a conventional xanthating baratte (Test F) and a portion was dropped into the ribbon blender (Test G).

Test F illustrates the conventional process. Carbon disulfide was added to the baratte and the baratte was revolved. After approximately minutes the xanthate sulfur substitution had reached 27% (based on the weight of cellulose charged to the steeping press). The xanthated alkali cellulose was then introduced into the mixer. The mixer had previously been charged with proper quantities of sodium hydroxide solution to produce a viscose containing 6.25% cellulose and 5.75% sodium hydroxide. After about 90 minutes of agitation, cyclohexylarnine was added. Mixing was continued for about another 60 minutes. The viscose solution was then removed from the mixer and permitted to ripen. During ripening it was filtered and deaerated. The spinning solution was then pumped to the spinning machine.

In Test G the ribbon blender was sealed, evacuated to about 20 inches of mercury (below atmospheric pressure) and the desired amount of carbon disulfide for both dry phase and dough phase xanthations was admitted to the vessel. After 30 minutes of reacting in the dry phase, a 16.2% Xanthate sulfur substitution had occurred. A dilute solution of sodium hydroxide was then added to form the dough having a cellulose content of about 12.5%. The dough phase xanthation was then conducted until the total of xanthate sulfur substitution had reached 26.7%. Water was then added to form the viscose spinning solution. Approximately 0.15% cyclohexylamine was then added and mixing continued for 15 minutes. The viscose solution was then removed from the ribbon blender and permitted to ripen. During ripening it was filtered and deaerated. The spinning solution was then pumped to the spinning machine. The following table compares Tests F and G.

Table III Test F Test G Viscose Composition Conven Ribbon tlonal Blender" Percent Cellulose 6. 25 6. 25 Percent Caustic 5. 75 5. 75 Percent Xanthate Substitution Accomp. in Dry Crumb Stage 27.0 16. 2 Percent Xant ate Substitution Accomp. in Dough Phase 10.5 Percent of Total Xnnthate Substitution Aceomp.

in Dough phase 0 89.3 Total Percent Xanthate S Dlssolving Stage- 27.0 20. 7 Slashed Yarn Properties (1650 Denier):

Dry Tenacity (g. p. d.) 4.21 4. 27 Dry Elongation (percent) 10.2 10.0 Tire Cord Properties (2 Ply Cord):

Twist (singles) 11.3 11.2 Twist (cord) 10.6 10.4 Tenacity Conditioned (g. p. d.). 3. 37 3.33 Tenacity Ovcn Dry (g. p. 3. 75 3. 71 Elongation at lbs. (Conditioned). 8. 5 8. 5 D. B. Fatigue (Minutes) 300 454 it will be observed that, although there is little difference in tenacity, the resistance of the cords to fatigue was improved by over 50% by splitting the xanthation in accordance with the process of this invention. The level of fatigue resistance values is higher than in previous examples because cotton linter cellulose was used, greater total percent xanthate substitution occurred and cyclohexylamine was added to the spinning solution.

EXAMPLE 4 This example illustrates the necessity of adhering to critical limitations to avoid adverse effects on filterability when preparing viscose spinning solutions in a ribbon blender. The filterability was determined for viscoses adjusted to the same contents of cellulose and caustic soda, as indicated in the last line of Table IV.

Alkali cellulose was prepared by steeping cellulose in the form of sheets of cotton linters, for 1 hour in 18% aqueous NaOH at 25 C. The alkali cellulose was pressed to a press weight ratio of 3.5 to 1, shredded and aged to obtain a viscose viscosity of 33:3 poises (measured at 20 (3.). The alkali cellulose crumbs were charged into a ribbon blender which was sealed, evacuated to about 20 inches of mercury (below atmospheric pres sure) and the desired amount of carbon disulfide for both dry phase" and dough phase xanthations was admitted to the vessel. The details of four tests, in which the ex tent of dry phase" xanthation was systematically varied, are recorded in Table 1V below. The results indicate the critical requirement that must be imposed on the dry phase" xanthation. Slight reduction (Test H) or slight increase (Test K) in the amount of dry phase" xanthation to a percentage of xanthate substitution outside the previously mentioned limits results, after dough phase" xanthation and subsequent dilution, in a poorly-filterable, undesirable viscose spinning solution.

Table IV Xanthating Conditions Test Test Test Test H I J K "Dry" Phase:

Xanthation Temperature 0 25 25 25 25 Xanthation Time (Min 30 45 Percent GS; Used 40 40 40 40 Percent Cellulose in Alk Cellulose. 2t 5 26.5 26.5 26.5 Percent NaOH in Alkali Cellulose... 15.7 15. 7 i5. 7 15. 7 Percent Xanthate Substitution in Dry Phase 12.5 17. 4 i9. 2 20. 2 Dougb" Phase:

Xanthation Temperature C.)..-... 24-26 24-26 24 26 24-26 Xanthation Time (Min.).. 75 75 75 75 Time for Caustic Addition (Min.) 7 7 7 7 Caustic Concentration (Percent NaOII) 1O 10 1D 10 Percent Cellulose in "Dough" 10. 5 10. 5 10. 5 10. 5 Percent NaOH in Dough" 7.4 7.4 7. 4 7.4 Percent Xanthate Substituti comp. in Dough" phase 10.7 5. 2 3. 5 3.2 Final Dilution:

Dilution Temperature C.) 26 26 26 26 Dilution Time (Min.) 30 30 30 30 Time for Water Addition (Min) 10 10 10 10 Percent Cell. in Viscose (Approx)... 6.25 6. 25 5. 25 6. 25 Percent NaOH in Viscose (ApproX.) 5. 75 5. 75 5. 75 5.75 Percent Xanthate Substitution (Total) 23. 2 22. 6 23.0 23. 4 Viscose Properties:

Percent Cellulose in Viseose.- 5. 25 I3. 33 6. 44 6. 28 Percent NaOH in Viscose..- 5. 71 5.74 5.71 5.82 Viscose Filterabillty (tor visc adjusted to contain 7% cellulose and 5% N aOH) 285 431 528 238 The invention has been illustrated by the use of bobbin and bucket processes for spinning high tenacity, fatigue resistant yarns which are especially desirable for tire cord. The same result is obtained with the conventional continuous process. The invention makes possible the production of yarn of high fatigue resistance regardless of the spinning method employed. Furthermore, the advantages of split xanthation are achieved in accordance with this invention without impairment of the filterability of the viscose.

This process is also advantageous in the spinning of textile yarn. By splitting xanthation, yarn of improved luster and better color is obtained in comparison to the textile yarn produced from conventionally xanthated viscose.

Other advantages result from the use of this process. When using conventional xanthating and mixing equipment, greater productivity is obtained from a baratte because of the shorter xanthation cycle. Also, because of the decreased amount of carbon disullide used in the baratte, cleaning the baratte, which had been a timeconsuming and difiicult operation, can be performed relatively quickly and easily. By using this process more efiicient reaction with carbon disulfide seems to result. This lowers the carbon disulfide content of the yarn after spinning and this reduces the ventilation problem con siderably.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is:

1. A split xanthation process which comprises the steps of partially xanthating alkali cellulose with carbon disulfide in a dry phase to a xanthate sulfur substitution of from 13% to 19%, mixing the partial xanthate with dilute aqueous caustic solution to a cellulose content of 4% to 15%. and mixing this xanthate mixture with carbon disulfide until an additional Xanthate sulfur substitution of at least 10% of the total substitution ultimately obtained has occurred.

2. A split xanthation process which comprises the steps of partially xanthating alkali cellulose with carbon disulfide in a dry phase to a Xanthate sulfur substitution of from 14% to 19%, mixing the partial xanthate with dilute aqueous caustic solution to form a dough having a cellulose content of 10% to and mixing the dough with carbon disulfide until an additional xanthate sulfur substitution of at least 10% of the total substitution ultimately obtained has occurred in the dough phase.

3. A split xanthation process which comprises the steps of partially xanthating alkali cellulose with carbon disulfide in a dry phase to a xanthate sulfur substitution of at least 13%, mixing the partial xanthate with dilute aqueous caustic solution to form a dispersion having a cellulose content of 4% to 10% and mixing the dispersed xanthate with carbon disulfide until an additional xanthate sulfur substitution of at least 10% of the total substitution ultimately obtained has occurred in the dispersion phase.

4. A split xanthation process which comprises the steps of partially xanthating alkali cellulose with carbon disulfide in a dry phase to a xanthate sulfur substitution of at least 13%, mixing the partial xanthate with dilute aqueous caustic solution to form a dispersion of 4% to 10% cellulose content having approximately the concentration of cellulose and alkali desired in the final viscose and finally mixing the dispersed xanthate with carbon disulfide until an additional xanthate sulfur substitution of at least 15% of the total substitution ultimately obtained has occurred in the dispersion phase.

5. A split xanthation process which comprises the steps of mixing alkali cellulose in a dry phase with a part of the total carbon disulfide required for xanthation and continuing the mixing until a xanthate sulfur substitution of at least 13% has occurred, mixing the partial xanthate with aqueous caustic solution to form a dispen sion having a cellulose content of 4% to 10% and an alkali content of 4% to 8%, and mixing the dispersion with the remaining part of the carbon disulfide until an additional xanthate sulfur substitution of at least 15% of the total substitution ultimately obtained has occurred in the dispersion phase.

6. A split xanthation process which comprises the steps performed in a single vessel of mixing alkali cellulose in a dry phase with at least 27.5% carbon disulfide, based on the weight of cellulose, and continuing the mixing until a xanthate sulfur substitution of 13% to 19% has occurred, adding sutficient dilute aqueous caustic solution within not over 10 minutes to form a dough having a cellulose content of 10% to 15%, continuing the mixing until an additionai xanthate sulfur substitution of at least 10% of the total substitution ultimately obtained has occurred in the dough phase, and finally diluting the dough to form a viscose of the desired cellulose and alkali content.

References Cited in the file of this patent UNITED STATES PATENTS 1,656,120 Kempter Jan. 10, 1928 FOREIGN PATENTS 314,504 Great Britain Nov. 28, 1930 370,772 Great Britain Apr. 14, 1932 

1. A SPLIT XANTHATION PROCESS WHICH COMPRISES THE STEPS OF PARTIALLY XANTHATING ALKALI CELLULOSE WITH CARBON DISULFIDE IN A DRY PHASE TO A XANTHATE SULFUR SUBSTITUTION OF FROM 13% TO 19%, MIXING THE PARTIAL XANTHATE WITH DILUTE AQUEOUS CAUSTIC SOLUTION TO A CELLULOSE CONTENT OF 4% TO 15%, AND MIXING THIS XANTHATE MIXTURE WITH CARBON DISULFIDE UNTIL AN ADDITIONAL XANTHATE SULFUR SUBSTITUTION OF AT LEAST 10% OF THE TOTAL SUBSTITUTION ULTIMATELY OBTAINED HAS OCCCURED. 